1. Field of the Invention
This invention relates to integrated circuit fabrication and, more particularly, to silicon nitride deposition techniques.
2. Description of the Related Art
The following descriptions and examples are given as background information only.
Silicon nitride layers are commonly fabricated within microelectronic devices for a variety of reasons. For example, in some embodiments, silicon nitride may be used as a dielectric to prevent an electrical connection between two materials. In addition or alternatively, silicon nitride may be used as an etch stop or polish stop. In some cases, silicon nitride may be used as a diffusion barrier to prevent impurities within one layer from diffusing into other layers of a microelectronic device. In yet other cases, silicon nitride may be used to prevent impurities external to the microelectronic device from affecting the device. In any case, a common technique for fabricating a silicon nitride layer within microelectronic devices is to generate a plasma of silane (SiH4) and ammonia (NH3) and expose a microelectronic topography to such a plasma. In general, such a process is conducted at a temperature equal to or greater than approximately 400xc2x0 C. In some cases, however, fabricating a silicon nitride layer at such a temperature may undesirably affect the operation of a device. For example, a device having magnetic structures may be undesirably affected by a processing temperature greater than approximately 300xc2x0 C. or, more specifically, greater than approximately 250xc2x0 C., in some cases. In particular, a relatively high temperature may alter the magnetic direction or the strength of magnetization within the magnetic layers of a device. In some embodiments, such a high processing temperature may cause individual magnetic layers within a structure to interdiffuse, causing the properties of the magnetic layer to change or render the magnetic layers non-magnetic.
Consequently, in some cases, the deposition technique described above is conducted at a temperature that is less than or equal to approximately 300xc2x0 C. Conducting the deposition technique at such a relatively low temperature, however, typically results in a high concentration of diatomic hydrogen molecules within the deposited film. Such diatomic hydrogen molecules may he susceptible to moving within the layer upon the application of heat during subsequent processing. In general, the movement of diatomic hydrogen within a layer will cause the atomic structure within the layer to change, causing a stress change within the layer. The magnitude of such a stress change may be dependent on the concentration of diatomic hydrogen molecules within the layer, the temperatures to which the layer is exposed, and the duration for which the layer is exposed to high temperatures. As such, in cases in which a relatively high concentration of diatomic hydrogen exists, the potential for a particularly large stress change may be imminent. In some cases, the stress change may be so severe that the layer cracks, exposing underlying portions of the topography and/or rendering the topography to be susceptible to the introduction or diffusion of impurities within the topography.
Therefore, it may be advantageous to develop a method which deposits a silicon nitride layer at a relatively low temperature without forming a substantially high concentration of diatomic hydrogen molecules within the layer. Such a method may be particularly beneficial for controlling the degree of stress change within the layer during subsequent processing.
The problems outlined above may be in large part addressed by a method which deposits a silicon nitride layer from a plasma generated from diatomic nitrogen gas. More specifically, the method may include creating a plasma from a gas mixture which includes diatomic nitrogen gas and a gas comprising silicon. In some embodiments, the ratio of diatomic nitrogen gas to silicon-containing gas within the mixture may be between approximately 0.5:1 and approximately 10:1. Larger or smaller ratios of the gases, however, may be used for the method described herein, depending of the parameters of the deposition process. In any case, the method may further include exposing a microelectronic topography to the plasma to form a silicon nitride layer thereon. In general, the microelectronic topography may include any microelectronic topography, including those topographies that include structures for semiconductor devices and/or magnetic devices.
In some cases, the silicon nitride layer may serve as a passivation layer for the topography of the microelectronic topography. Alternatively, the silicon nitride layer may serve a different function within the topography of the microelectronic topography, such as a dielectric layer, etch stop layer, and/or polish stop layer, for example. In some cases, the method may further include depositing a silicon dioxide layer upon the microelectronic topography prior to the deposition of the silicon nitride layer. In such an embodiment, the deposition of the silicon dioxide layer may be conducted within the same reaction chamber as the deposition of the silicon nitride layer. In other embodiments, however, the deposition of the silicon dioxide layer may be conducted in a different reaction chamber than used for the deposition of the silicon nitride layer. In either case, the method may be conducted in a high density plasma reaction chamber, in some embodiments. Alternatively, the method may be conducted in other types of plasma reaction chambers.
In some embodiments, it may be advantageous to deposit the silicon nitride layer at a temperature less than or equal to approximately 300xc2x0 C., or more specifically, between approximately 200xc2x0 C. and approximately 250xc2x0 C. In particular, it may be advantageous to deposit the silicon nitride layer at a relatively low temperature in order to minimize the generation of diatomic hydrogen molecules with the silicon nitride layer. In other cases, however, the deposition of the silicon nitride layer may be conducted at a temperature greater than approximately 300xc2x0 C. In general, a layer has a certain amount of stress upon deposition. The stress within the layer may be altered, however, by subsequent processing of the topography on which the layer is formed. For example, heating a silicon nitride layer may cause movement of diatomic hydrogen molecules arranged within the layer, causing a stress change within the layer.
The deposition technique described herein, however, may form a relatively low concentration of diatomic hydrogen molecules within a silicon nitride layer. In particular, the deposition technique may create a silicon nitride layer having a concentration of diatomic hydrogen that is at least one order of magnitude lower than a concentration of diatomic hydrogen within a silicon nitride layer alternatively formed from a plasma generated from ammonia. Such a difference in the generation of diatomic hydrogen molecules within silicon nitride layers of the two distinct techniques may be even larger when the deposition methods have both been conducted at a temperature less than or equal to approximately 300xc2x0 C. For example, in some cases, the concentration of diatomic hydrogen within the silicon nitride layer formed using the method described herein may be at least three orders of magnitude lower than the concentration of diatomic hydrogen within a silicon nitride layer formed from a plasma generated from ammonia.
In any case, the method may further include processing the microelectronic topography at a temperature greater than or equal to approximately 250xc2x0 C. subsequent to the deposition of the silicon nitride layer. Such a step of subsequently processing the microelectronic topography may produce a stress change of less than approximately 1.0xc3x971010 dynes/Cm2 within the silicon nitride layer. In other words, the method may include heating the microelectronic topography such that a stress change of less than approximately 1.0xc3x971010 dynes/cm2 is induced within the silicon nitride layer. In some cases, the stress change is less than approximately 1.0xc3x97109 dynes/cm2, or more specifically, less than approximately 2.0xc3x97108 dynes/cm2. In any case, the stress change may be directed toward either a tensile stress condition or a compressive stress condition within the silicon nitride layer.
In general, the step of subsequently processing the microelectronic topography may include any processes which are conducted at a temperature greater than approximately 250xc2x0 C., including processes within the fabrication or assembly of the microelectronic topography. For example, the step of subsequently processing the microelectronic topography may include annealing the microelectronic topography. In addition or alternatively, the step of subsequently processing the microelectronic topography may include depositions of other layers and/or etching layers of the microelectronic topography. As such, in some embodiments, the steps of subsequently processing the microelectronic topography may include a plurality of processes conducted at temperature greater than approximately 250xc2x0 C. subsequent to the step of forming the silicon nitride layer. In other embodiments, however, the step of subsequently processing the microelectronic topography may include only a single processing step.
There may be several advantages to fabricating a silicon nitride layer using the method described herein. In particular, the method may generate a relatively low concentration of diatomic hydrogen molecules within the silicon nitride layer upon deposition. In turn, the layer may undergo a relatively small degree of stress change during subsequent processing of the topography including the silicon nitride layer. Consequently, a silicon nitride layer deposited using the method described herein may be less prone to crack. Therefore, a topography including a silicon nitride layer deposited by the method described herein may be less susceptible to the introduction or diffusion of impurities within the topography.